It has been long realized in a general sense that the efficiency of a heat exchanger increases at higher temperatures. Counterbalancing this desirable mode of operation, however, is an attendant increase in heat losses at elevated temperatures. Prior art in the industrial area is replete with solutions to this problem, but factors, such as, cost, weight of materials, design geometries and types of materials generally are not significant limiting considerations. The heat loss problems related to contemporary solar fluid heaters for smaller scale users, on the other hand, do not enjoy the solution flexibility existing in heavier industrial applications. Cost, compactness, weight and ease of mounting are a few of the major factors to be considered when addressing the problems of heat loss in these latter mentioned applications.